Right-Sizing: When You Pay to Ship Air

What is right-sizing?

Right-sizing — also known as empty-space or volume optimization (German: Leerraumoptimierung) — is the most effective lever in packaging optimization. It answers a question that sounds simpler than it is: which set of box sizes ships all orders with the least inefficiency? The key word is all. The interesting question isn't "which box fits this one order?", but which box assortment best fits a whole year of wildly varied orders — from a single item to a full basket. Dimensioning boxes so that as little air as possible travels along is exactly what right-sizing means.

Why empty space can't be optimized on its own

You never optimize empty space alone. Four levers are interconnected — push one too far and the others suffer:

The extremes show the conflict: "one box for everything" needs only a single size and minimal shipments, but wastes the most material and air. "One box per order" would have zero empty space and minimal material, but with infinitely many variants it would be operationally impossible. The good assortment lies in between — and is always a compromise.

Box-assortment optimization: why spreadsheets fail

Even optimally packing a single order is a three-dimensional packing problem — and such problems are considered "NP-hard": for realistic sizes, an exact solution can't be computed in reasonable time. For ten items, box choice, sequence, orientation and parcel split combine into over 10 billion possible arrangements. Across an entire assortment and many orders, there is no way to compute it all — a spreadsheet gives up here.

How AI finds the right box assortment

Problems like this are solved today with AI-based methods that work from two directions. One searches strategically across thousands of possible box sets, discarding weak ones and refining promising ones. The other checks operationally whether each order fits a proposed set and how much empty space remains. Both compute against the real order history, not against assumptions or average baskets — so the result is not a theoretical optimum, but an assortment that proves itself on the orders actually shipped.

Case 1: from standard box to tailored assortment

Flaconi wasn't optimized yet: fewer than ten packaging specifications were meant to cover a fast-growing range. This is exactly where the lever is biggest. After optimization, transport volume fell by around 30%, packaging costs by 35% and packaging-related CO₂ by 30% too — while around 100 additional parcels were processed per employee per day.

“Thanks to the size and packaging optimization, we reduced our CO₂ emissions in this area by 30% and cut our packaging procurement costs by 35%.”
— Kurt Westphal, Team Lead Operations Excellence, Flaconi (reference)

Case 2: already optimized — is more worth it?

The second shipper (B2B e-commerce, around a million orders a year) had optimized its 6-box assortment in-house years ago. Its question wasn't "how much can we save?", but: how good is that optimization really — and what would running more or fewer box sizes do to shipping logistics?

The average fill rate of 59.1% looks solid. Broken down per box, though, it tells a different story: the two smallest boxes are only 38% and 43% full — more than half is air. And those two carry 35% of all shipments. So the biggest savings potential sits in the small-order segment — exactly where the average hides it.

More or fewer box sizes?

The same assortment, recomputed with 4 to 8 sizes: more sizes raise the fill rate — but every extra size is one more SKU (stock-keeping unit) in the warehouse, on the packing line and in planning. Seven boxes hit the sweet spot at +4.4 percentage points; the eighth added only +0.9 pp. Right-sizing means "the right number", not "as many as possible".

What right-sizing delivers: lower shipping, board and CO₂

Even for the already-optimized shipper, those +4.4 percentage points turn into tangible effects over a shipping year: roughly 50 truckloads, about 40,000 m² of corrugated board and around 150 t of CO₂ less per year.* Smaller boxes also cut shipping costs directly, because many carriers bill by volumetric weight. Beyond a certain scale, right-sizing is therefore not just a packaging topic but a supply-chain one — and a direct lever to reduce packaging costs.

Alternatives and limits

A good assortment lowers the baseline need — but it's rarely the only building block. Alongside it stand on-demand packaging (boxes are made to height or fully to size per shipment), height reduction on the packing line (the box is cut down to the actual fill height) and simply doing without unnecessary void fill. Whether these approaches combine sensibly with an optimized assortment, however, depends heavily on the shipper's profile. On-demand packaging, for example, plays to its strengths with great size variety and moderate volumes, but quickly hits limits in high-volume B2C e-commerce: machine cost, throughput and cycle time per parcel are often hard to reconcile with very large shipment volumes. On top of that come switching costs — existing stock, retooling the packing line, training — that only pay off over volume.

A look ahead: after volume comes material. When around 87% of shipments in one box weigh under 5 kg, a lighter corrugated grade can be used there; conversely, for the few heavy shipments a reinforced quality pays off against transport damage. Assortment optimization lays the data foundation for this — it shows which box carries which weights.

Packaging optimization and the PPWR

What used to be a cost question is becoming an obligation: the EU Packaging Regulation (PPWR) caps the empty-space ratio for transport and e-commerce packaging at a maximum of 50% — optimize early and you meet the requirement while saving at the same time. We've laid out the deadlines, articles and calculation details on our PPWR page.

Edge cases every optimization knows

• Small but heavy. A lighter box saves CO₂ — but can break the empty-space limit, because heavy small items leave a lot of air.
• Split shipments. Splitting a large order evenly across parcels satisfies the rule — but often defies common sense.
• The human factor. What is optimal on paper has to stay practically packable on the line.